1. Field of the Invention
The present invention relates to a keyboard apparatus used as an apparatus with which to enter characters, etc. and, more particularly, to a thin keyboard apparatus suited for use with a notebook-size computer.
2. Description of the Related Art
FIG. 6 is a sectional view showing a key of a conventional keyboard apparatus 20 as observed sideways. The keyboard 20 is constituted primarily by a key top 1, supporting members 2 and 3, a housing member 31, a membrane switch 4, a metal plate 5, and an elastic member 6.
The key top 1 is provided with a total of four retaining portions 1a, 1a, 1b, and 1b which are located at the four corners of the rear surface of the key top 1 to support the supporting members 2 and 3.
The supporting members 2 and 3, which support the key top 1, are installed so that they intersect with each other, and attached by a shaft 8 provided at the center of side faces thereof so that they may circularly move. The supporting member 3 disposed on the inner side has a round through hole 9 formed at the center thereof as shown in FIG. 5. The supporting member 2 disposed on the outer side is shaped like "C" as shown in FIG. 5. The distal ends of the supporting members 2 and 3, respectively, have columnar protuberances 2a, 2a, 3a, and 3a projecting outward. The protuberances 2a are disposed and inserted in the retaining portions 1b so that it may slide back and forth, while the protuberances 3a are fitted in the retaining portions 1a and rotatably supported therein.
The columnar protuberance 2b formed on the proximal end of the supporting member 2 is rotatably attached to a retaining portion 32 of the housing member 31, while the columnar protuberance 3b formed on the proximal end of the supporting member 3 is slidably disposed in a recess 33. In the supporting member 3, a shaft (not shown) provided between legs 3c and 3c is locked by a retaining member protruding from the housing member 31 so as to prevent the supporting member 3 from coming off the housing member 31.
The bottom surface of the housing member 31 is provided with the membrane switch 4 sandwiched between the housing member 31 and the metal plate 5.
The membrane switch 4 is formed of three layers of film sheets (not shown), two layers, namely, the top and bottom layers, of which being provided with printed electrode patterns formed on the opposing inner surfaces thereof. A film type spacer is inserted between the two sheets of the membrane switch 4, and the spacer has holes beneath the respective key tops 1 so that the top and bottom electrodes conduct when the key tops are depressed. The membrane switch 4 is further provided with a plurality of apertures running through the three layers to fasten the housing member 31 and the metal plate 5.
The metal plate 5 formed of a metal constituent such as an aluminum constituent is provided below the bottom surface of the membrane switch 4.
The metal plate 5 is provided with a plurality of apertures in which a plurality of protuberances of the housing member 31 are inserted, the protuberances being formed at the same positions as the apertures. The protuberances of the housing member 31 that jut out from the underside of the metal plate 5 are partially melted to fasten the housing member 31 and the metal plate 5.
The elastic member 6 is disposed at the center of the keyboard apparatus 20. The elastic member 6 passes through the round through hole 9 formed in the housing member 31 and rested on the top surface of the membrane switch 4 without being bonded. The diameter of the through hole formed in the housing member 31 is smaller than the diameter of the bottom end of the elastic member 6, so that the elastic member 6 does not come off the housing member 31 even if it is not secured by bonding.
The elastic member 6 is formed of a constituent providing an urging force so that it is always urged upward.
The conventional keyboard apparatus 20, however, is too thick to satisfy the recent demand for achieving further thinner notebook-size computers.
Normally, in a keyboard apparatus used with a notebook-size computer, a thickness X of a key top has been set to 3 mm at the minimum and a travel distance Y of the key top 1 has been set to 3 mm at the minimum, and making the keyboard apparatus further smaller has been restrained in consideration of the feel and ease of use. Hence, a study has been conducted to determine if any of the members from the housing member 31 and below can be omitted because it was impossible to further decrease the thickness X and the travel distance Y.
As a study result, a method has been proposed in which the retaining portions that support the supporting members 2 and 3 are directly supported by the metal plate 5, thus eliminating the housing member 31. This, however, has been posing a problem of a higher machining cost because directly forming the retaining members on the metal plate 5 requires that the metal plate 5 be cut and raised to form retaining portions 41, 41, 42, and 42 as shown in FIG. 7.
In addition, to install the supporting members 2 and 3, protuberances 3b and 3b of the supporting member 3 are first hooked to the retaining portions 42 and 42, then the protuberances 2b and 2b of the supporting member 2 are inserted in the retaining portions 41 and 41 through openings 41a and 41a. At this time, the protuberances 2b and 2b must be fitted in with a strong force because the retaining portions 41 and 41 are shaped like arches. This has been presenting a problem in that the assembly takes more time and is more difficult than in the example of the conventional art shown in FIG. 6.